As was disclosed in co-pending application Ser. No. 906,057, by the same inventor and assigned to the same assignee of the instant application, attempts have been made to transmit to an equipment under test stimuli for eliciting therefrom responses which would indicate the operational status of the equipment, after the responses are compared with expected results. Since the number of equipment which may be tested is dependent upon the rate at which the patterns are generated from the automatic testing instrument, it was clear that the faster an automatic testing instrument can send out the stimuli, a greater number of equipment may be tested within a certain given time. In the above-noted co-pending application, a stimulator which can generate stimuli at both high and low data rates is disclosed. To round out the automatic testing instrument, a corresponding response memory, or as discussed in the co-pending application--a responder, is needed.